The idea is that, if the map is pirated and published elsewhere without permission, the places that don't exist establish the copyright.

There's an interesting thread about matters of this kind -- including "copyright traps" on maps, per the process which you describe, which ultimately became real places -- on the Fortean Times discussion forum.

Included there, is the strange tale of the supposed Sandy Island -- allegedly several hundred miles east of Australia, and measuring fifteen miles by three. It was recently found that this "island", which has featured on maps for quite a long time, actually doesn't exist. Discussion is generated thereby, as to whether it was a copyright trap gone wrong; or pure human error; or whether at the island's alleged discovery in the 1870s, it was a sandbar then existing, but subsequently covered by the sea; or something else?

Deliberate distortion of, and putting wrong info on, maps for the use of the public happened rather a lot in the former Soviet Union; this being done at the behest of the authorities, to thwart would-be spies. It was maddening for local citizens and (blameless) foreigners, who were just seeking to get to where they wanted to go. As regards the USSR, one feels that the kindest possible verdict is "they were a funny lot".

If I have things rightly, the New Zealand town of Waikikamoukau does not actually exist; it was invented to gently take the mickey out of NZ place names?

Yes Waikikamukau is fictional, sort of a placeholder name for a small town out the back of beyond.

Sounds like a parallel with Germany’s “Krähwinkel”; and “Hotzeplotz” and “Eytschischok” in Yiddish – fictitious names symbolising the general picture re those milieus, of a remote, dozy, benighted back-end-of-nowhere settlement.

'Boondocks' has been used all of my life, but I was surprised to see that is really is so recent.

From AnswerBag, but I found similar information on other sites:

The expression was introduced to English by American military personnel serving in the Philippines during the early years of the 20th century. It derives from the Tagalog word "bundok", meaning "mountain".

One said 1945, but if it is from the Philippines it could be far earlier. My grandfather was an agricultural advisor there in the early 1900s, so I know we (US) had a presence there. (I don't know how reliable AnswerBag is - better than AskYahoo, I hope!)